The invention encompasses methods of depositing silicon nitride on sodalime glass surfaces and to methods of forming field emission display devices.
Flat-panel displays are widely used to visually display information where the physical thickness and bulk of a conventional cathode ray tube is unacceptable or impractical. Portable electronic devices and systems have benefitted from the use of flat-panel displays, which require less space and result in a lighter, more compact display system than provided by conventional cathode ray tube technology.
A particular type of flat-panel display is, the field emission flat panel display. In a field emission flat-panel display, an electron emitting cathode plate is separated from a display face or faceplate at a relatively small, uniform distance. The intervening space between these elements is evacuated. Field emission displays have the outward appearance of a CRT except that they are very thin. While being simple, they are also capable of very high resolutions. In some cases, they can be assembled by use of technology already used in integrated circuit production.
Field emission flat-panel displays utilize field emission devices, in groups or individually, to emit electrons that energize a cathodoluminescent material deposited on a surface of a viewing screen or display faceplate. The emitted electrons originate from an emitter or cathode electrode at a region of geometric discontinuity having a sharp edge or tip. Electron emission is induced by application of potentials of appropriate polarization and magnitude to the various electrodes of the field emission display device, which are typically arranged in a two-dimensional matrix array.
A field emission display device 10 is illustrated schematically in FIG. 1. Device 10 comprises a faceplate 12 comprising a transparent conductor. Underlying faceplate 12 are phosphor dots 14. A spacer 16 is provided to space faceplate 12 from a series of column electrodes 18 and emitters 20. Column electrodes 18 and emitters 20 overlay row electrodes 22, which in turn overlay a baseplate 24.
Baseplate 24 is typically made out of sodalime glass, and typically comprises a layer of silicon nitride formed between baseplate 24 and emitters 20. The silicon nitride is deposited to provide a buffer layer between glass and subsequent layers. This results in better stress control and adhesion between the subsequent metal, emitter and grid layers. Another advantage of this buffer layer is that it can cap or prevent impurities within the glass from entering into other parts of the device structure. Emitters 20 are thus at least partially supported by the layer of silicon nitride. The silicon nitride can be deposited by a number of conventional methods, including, for example, a plasma enhanced chemical vapor deposition process utilizing silane and ammonium gasses. An example deposition method comprises placing a glass substrate within a reactor. The pressure within the reactor is maintained at about 1000 mTorr, and a power within the reactor is maintained at about 500 watts. A mixture of SiH4 and NH3 is flowed into the reactor. A flow rate of the SiH4 is 100 standard cubic centimeters (sccm). A flow rate of the NH3 is 450 sccm. The deposited silicon nitride disadvantageously has a tensile stress which renders the silicon nitride prone to scratching and cracking.
It would be desirable to develop alternative methods of forming a silicon nitride coated baseplate wherein the silicon nitride does not have a tensile stress.
The invention encompasses methods of treating sodalime glass surfaces for deposition of silicon nitride and methods of forming field emission display devices.
In one aspect, the invention encompasses a method of treating a sodalime glass surface for deposition of silicon nitride. A surface of the glass is cleaned with a detergent and contacted with a solution comprising a strong oxidant to remove non-silicon-dioxide materials from the surface and from a zone underlying and proximate the surface.
In another aspect, the invention encompasses a method of depositing silicon nitride. A surface of a sodalime glass substrate is contacted with a solution comprising sulfuric acid and hydrogen peroxide to remove non-silicon-dioxide materials from the surface and from a zone underlying and proximate the surface. The surface is then exposed to a mixture of SiH4, NH3 and H2 to deposit silicon nitride on the surface.
In another aspect, the invention encompasses a method of depositing silicon nitride on a sodalime glass surface. A sodalime glass surface is provided and contacted with a detergent solution. The detergent solution is agitated across the sodalime glass surface and then removed from the sodalime glass surface by rinsing it in deionized water at about 80xc2x0 C. After removing the detergent solution, the sodalime glass surface is contacted with a sulfuric acid solution to remove nonsilicon-dioxide materials from the surface and from a zone underlying and proximate the surface. The sulfuric acid solution is then removed from the sodalime; glass surface. After removing the sulfuric acid solution, nitride is deposited on the sodalime glass surface.
In another aspect, the invention encompasses a method of forming a field emission display device. A base plate is formed. The forming of the base plate comprises the following steps. A base plate substrate is provided. The base plate substrate comprises a sodalime glass surface having a first concentration of an undesired chemical. The sodalime glass surface is contacted with a detergent solution. The detergent solution is agitated across the sodalime glass surface and then removed. After removing the detergent solution, the sodalime glass surface is contacted with a sulfuric acid solution to extract at least some of the undesired chemical from the sodalime glass surface and from a zone underlying and proximate the surface. The sulfuric acid solution and the extracted undesired chemical are removed from the sodalime glass surface. After removing the sulfuric acid solution, the sodalime glass surface comprises less than the first concentration of the undesired chemical. After removing the sulfuric acid solution, depositing nitride on the sodalime glass surface to form a base plate. Emitters, at least partially supported by the silicon nitride of the base plate, are formed.